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Old 09-12-2009, 12:49 AM   #11
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Re: Grounding the inverter question

Thanks for the detailed advice & instruction Redbear!
Today I finished the off-grid power. What I ended up doing was to run short leads throughout the whole system. The leads on the batteries are short, the distance from the batteries to the inverter is less than 48", & I added a circuit breaker to the hot DC side. I used a 40A breaker as the cables are 4AWG & they fit this breaker (home depot electrician said it was fine to use). I did add a ground strap to the inverter to an area I drilled, sanded to bare metal & then bolted the strap on after spraying the metal with WD40 to protect it. The place I drilled thru is a steel lip that comes off of the wall that the seat belts mounted to & is very strong & thick steel (seat backs faced the wall). Are you saying I should remove this ground to avoid potential problems?
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Old 09-12-2009, 03:34 AM   #12
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Re: Grounding the inverter question

I hate to be that guy and all, but 1000 watts AC is 1000 watts DC, To get wattage you multiply volts times amps. Perhaps a better way to say it would be to get current (amps) you divide wattage by volts. You inverter is capable of 1000 watts. 1000 watts divided by 14.4 (which would be your alternator going full tilt boogie, not the battery voltage with the engine stopped) would be nearly 70 amps. Worse yet is that that is assuming 100% inverter efficiency which is not the case. The point is that that 40 amp circuit breaker is grossly undersized. If you want to get anywhere near the 1000 watt rating of your inverter you're going to need at least a 100 amp fuse and more than likely you will need a 120 amp or larger fuse to handle the current at maximum inverter output.
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Old 09-12-2009, 08:23 AM   #13
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Re: Grounding the inverter question

Ditto on the big fuse.

Rub through the positive cable insulation without a fuse {mounted very close to the batteries, you get a welder...or a fire. Depend on corroded body panel and frame connections for the ground, same deal.

That is the one thing I dread about my bread truck RV, fire.

2 nice extinguishers on board, fore and aft.
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Old 09-12-2009, 09:53 AM   #14
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Re: Grounding the inverter question

Quote:
Originally Posted by the_experience03
I hate to be that guy and all, but 1000 watts AC is 1000 watts DC, To get wattage you multiply volts times amps. Perhaps a better way to say it would be to get current (amps) you divide wattage by volts. You inverter is capable of 1000 watts. 1000 watts divided by 14.4 (which would be your alternator going full tilt boogie, not the battery voltage with the engine stopped) would be nearly 70 amps. Worse yet is that that is assuming 100% inverter efficiency which is not the case. The point is that that 40 amp circuit breaker is grossly undersized. If you want to get anywhere near the 1000 watt rating of your inverter you're going to need at least a 100 amp fuse and more than likely you will need a 120 amp or larger fuse to handle the current at maximum inverter output.
Bear with me - I am trying to understand what is going on here... The power setup I have is strictly off-grid solar like I mentioned & it will not be connected to the bus power/alternator in any way...It will be a seperate system completely... I will only be running a computer (the highest powered piece of equipment) & a few other office items, nothing else. Do I really need to have a 100 amp fuse inline?? I have read & talked to others that have told me they keep their off-grid setup completely seperate from the bus power, including no grounds whatsoever. Oh, & yea, I already have the fire extinguishers in place!
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Old 09-12-2009, 10:22 AM   #15
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Re: Grounding the inverter question

You have to account for all the energy stored in the battery, and the large cables the inverter require. The large cables will handle a much higher amperage.

A smaller wire will heat up, even smaller it will burn like a light filament then melt. So, you use big cables to avoid the heat and voltage loss.

The big cables can handle the amperage without heating up. Having them unfused is dangerous.
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Old 09-12-2009, 10:52 AM   #16
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Re: Grounding the inverter question

here is an online inverter calculator that will give you an idea of your needs, and what cable to use. looks pretty close to most specs I have seen, but when it comes to cabling I believe in overkill.

http://www.skingcompany.com/portable_power/calc2.htm
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Old 09-12-2009, 04:41 PM   #17
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Re: Grounding the inverter question

Quote:
Originally Posted by Ob1
here is an online inverter calculator that will give you an idea of your needs, and what cable to use. looks pretty close to most specs I have seen, but when it comes to cabling I believe in overkill.

http://www.skingcompany.com/portable_power/calc2.htm
I checked it out & if I am reading it correctly the draw will only be 13 amps at any given time with everything running... That is pretty low.
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Old 09-12-2009, 06:29 PM   #18
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Re: Grounding the inverter question

Your fuse and cable selection should be at least to 100% of the inverters rated power, not what your intended load is.
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Old 09-12-2009, 07:21 PM   #19
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Re: Grounding the inverter question

I am curious, what size Fire Extinguishers did you get? My guess would be the normal 10lb extinguishers. You might want to get a 30lb to back up your smaller ones. I know that the average person will never have to use their extinguishers, but in the off chance that you do, its better to have at least 1 BIG extinguisher to fall back on when you discharge the little ones.

My father use to know a Firefighter named Brian. Brian would go to companies and teach the employees how to put out fires so that they could do something to contain them while the Fire department was on their way... So, one hot LA day, he sets up a small pavement fire out in the parking lot of a business and in the course of his teaching shows how to put it out with a small extinguisher without problem. He resets it, and hands a new extinguisher to an employee and tells them to put it out, and for two or three fires, this works. Too bad that the heat of the day (around 90), plus the fires heat, have heated the tar in the pavement... So the last group uses their extinguisher to put out the fire, only it doesnt go out. She they call for help.

Brian grabs a fresh extinguisher, and empties it into the fire to no effect. Goes back to his truck and grabs another one...and another...and another. Seeing that he has a problem, he calls the Dispatcher and tells them that he needs One (1) Fire Truck to come to him to put out a "Small Parking Lot Fire". The Dispatcher types this in, and the computer says that its an industrial area and requires that they dispatch EVERY fire truck in the valley... Brian, just putting down the radio, started hearing siren after siren start up... A line of trucks shows up shortly after. When the lead truck pulled up, the Fire Chief steps off and walks over to Brian to find out whats going on. Brian explains and points to the 20 or so spent extinguishers that he used.

The Chief turns, walks over to Brian's truck and opens the back, where he pulls out a 50lb Extinguisher. Carries it to the fire and with one long squeeze of the handle, puts out the fire. Brian was heard to have muttered "I forgot that I had that..." to the Chief when he asked him why he didn't use it.

Moral of the story: 1) Have a large extinguisher handy even if you think that you will never use it. 2) When calling in a fire at an Industrial Complex, Expect alot of Peer Witnesses to see your screw-up.

Brian also did a demonstration about how Gasoline is hard to ignite... He took a cup of gasoline and dropped a lit cigarette into it while the room gasped in shock. When nothing happened, he continued his explanation while he lit up another, grabbed an eye dropper of gas and put a drop into a large stoppered bunsen burner, and started shaking it. After shaking it for about a minute, he pulls out the top stopper and drops in the cigarette and BOOM.... Little bits of paper and tobacco falling to the ground...

No more than Thirty (30) seconds later, People from around the building start showing up with first aid kits and wanting to know what the "Explosion" was...

Brian has a Reputation.
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Old 09-12-2009, 08:41 PM   #20
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Re: Grounding the inverter question

Quote:
Originally Posted by Ob1
Your fuse and cable selection should be at least to 100% of the inverters rated power, not what your intended load is.
I think I have it covered as the inverter is rated: Output current (peak) 25 A. This is covered by a GFI outlet & the breaker box is in between the battery bank & the inverter protecting & allowing me to shut off the power... This wire gauge is good for what I am running.
Thanks for all the info & the electrical lesson!
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